We have planned a conference, under the auspices of the New York Academy of Sciences, on the calciUM-dependent release of neurotransmitter substances from the presynaptic nerve terminal. Synaptic transmission is a fundamental processes in brain function but transmitter release mechanisms remain poorly understood. This conference will focus on nerve terminals but will draw on findings from other cell types in the discussion of the biophysical and pharmacological properties of nerve terminal calcium channels, the entry and distribution of calcium ions after the nerve impulse, the physiology of calcium-dependent transmitter release, and the mechanism whereby calcium triggers secretory vesicle fusion. In addition, new experimental techniques will be highlighted that allow direct experimentation on vertebrate nerve terminals. The intent of this meeting is to offer an opportunity for investigators in these fields to become aware of, and to contribute to each others interests and, by identifying gaps in our knowledge, to indicate promising lines of research. The importance of synaptic transmission to brain research in general, and the rapid advance of research on all aspects of the biology of calcium ions, make a focussed conference on this issue particularly timely.